Copolymer of glycidyl methacrylate and allyl glycidyl ether

ABSTRACT

Copolymers of glycidyl methacrylate and allyl glycidyl ether having pendant epoxy groups, having an inherent viscosity of at least about 0.25, preferably within the range of about 0.25 to about 0.38, and an epoxy equivalent of at least about 0.65 epoxide equivalent per 100g. of polymer are provided which upon admixture with a radiation-sensitive aryldiazonium salt provide compositions which exhibit improved sensitivity, curing rates and other properties. Articles for recording and storing information from a laser source and other articles such as microfilm are derived from such compositions by subjecting a coated substrate to an energy source of sufficient intensity to decompose the radiation-sensitive catalyst and thus effect polymerization via the epoxy groups of the copolymer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of copending application Ser.No. 509,674 filed Sept. 26, 1974, now abandoned, which is in turn adivisional of application Ser. No. 297,829 filed Oct. 16, 1972, nowabandoned.

BACKGROUND OF THE INVENTION

In U.S. Ser. No. 753,869, filed Aug. 20, 1968 entitled"Photopolymerization of Epoxy Monomers", now U.S. Pat. No. 3,708,296issued Jan. 2, 1973, there are disclosed novel compositions comprisingvarious epoxy materials and certain latent curing catalysts therefor.Such compositions are photosensitive and when exposed to an energysource such as actinic radiation yield epoxy polymers which arereceptive to ink and possess inherent toughness, abrasion resistance,adherence to metal surfaces, resistance to chemical attack, etc. and arethus valuable for many applications particularly those involvingformation of acid and alkali resist images for chemical milling, gravureimages, offset plates stencil-making, etc.

It has now been disclosed that a specific epoxide material, a copolymerof glycidyl methacrylate and allyl glycidyl ether, specially prepared,when utilized with the latent curing catalysts of said U.S. Pat. No.3,708,296 is unique in exhibiting superior photosensitivity, adhesionand other properties, may be rapidly cured after a short exposure to aenergy source without the additional application of thermal energy suchas heat and is readily prepared by a process as described hereinbelow.It has further been discovered that such superior properties of saidcopolymeric epoxide material renders it eminently suitable for use inthe recording and storage of information derived from a laser source,particularly as holograms.

U.S. Pat. No. 3,074,869 discloses epoxy resin prepolymers, includingpolyglycidyl methacrylate, cured with certain nitrosamines via a freeradical mechanism. Compositions containing this homopolymer however,following light exposure, must be heated to 140° C to cure or crosslinkthe polymer so that an image may be developed. Further, preparation ofthe homopolymer is tedious requiring 3 to 4 days of heating at 50° C toyield a useful polymerizable product.

The advantages of the copolymers of this invention over such prior arthomopolymers in ease of preparation and rapid curing and use withoutsubsequent heat are readily apparent and provision of such copolymersfulfills a need in the art for such products in terms of efficiency andsuperior properties. Moreover, as further illustrated hereinbelow, sucha homopolymer does not lead to products of photosensitivity comparableto that of the copolymer of the invention.

It is known to employ various presensitized substances including silverhalide film, bichromated gelatin and photopolymers such as photochromicspiropirans and compounds derived from barium acrylate, leadacrylate-acrylamide with photocatalyst solution comprising methyleneblue and sodium salts of various organic acids to record laserinterference patterns. Such disclosures appear in the literature atApplied Physics Letters, Vol. 15, No. 7, October, 1969 (p.201-203;Ibid., Vol. 14, No. 5, March, 1969 (p. 159-160).

None of these existing systems are without serious deficiencies eitherin terms of low resolution of images, instable image formation,difficulty and slowness in processing, short-life of systems employed orthe use of expensive silver salts.

The present invention provides substances for this purpose that aredevoid of the deficiencies listed above.

SUMMARY OF THE INVENTION

The present invention provides novel and unique copolymers of glycidylmethacrylate and allyl glycidyl ether having pendant epoxy groups andhaving an inherent viscosity of at least about 0.25, preferably withinthe range of about 0.25 to 0.38, and an epoxide equivalent of at leastabout 0.65 per 100g. of polymer derived from a process which comprisesadmixing the respective monomers, in the presence of a polymerizationcatalyst such as benzoyl peroxide, in a solvent which permits reflux ofthe reactants at a temperature below about 100° C.

The invention further provides novel polymerizable compositionscontaining, as latent curing catalysts, aryl diazonium salts which areradiation-sensitive and release an active catalyst upon the applicationof energy such as actinic radiation or a coherent beam of energy as froma laser source and the use of such compositions for the production ofarticles suitable for recording and storing information derived fromsuch an energy source.

DETAILED DESCRIPTION OF THE INVENTION I. Glycidyl methacrylate-allylglycidyl ether copolymers and preparation thereof

The copolymers of the present invention are characterized by having aninherent viscosity of at least about 0.25 and preferably within therange of 0.25 to 0.38, and an epoxide equivalent of at least about 0.65,preferably 0.65 to 0.74 epoxide equivalent per 100g. of polymer. As willbe illustrated hereinbelow, these parameters are of a critical naturesince copolymers that do not exhibit the specified parameters aredeficient for the purpose of the present invention.

The values of inherent viscosity herein are measured in butyronitrile at25° C unless otherwise pair/mm. viscosity is an indication of molecularweight and is determined according to the equation ##EQU1## where C =concentration of copolymer in grams per 100 ml. of solvent and 1n (η₁/η₀) = the natural logarithm of the relative viscosity of the dilutesolution.

As is well known in the art, inherent viscosity is an indication ofmolecular weight of polymers. Thus, molecular weights for the copolymersof this invention having an inherent viscosity of at least about 0.25will be at least about 3000 and copolymers having inherent viscositieswithin the preferred range of 0.25 to 0.38 will have molecular weightswithin the range of about 3000 to about 6000.

The present invention provides copolymers that must necessarily possessbalanced properties exemplified by the epoxide equivalent and inherentviscosity, the combination of which are critical and essential to derivethe properties of superior photosensitivity. Since the reacting monomerspossess both epoxide groups and ethylenically unsaturated double bondswhich are both capable of undergoing polymerization and/orcross-linking, it is possible to produce polymers exhibiting either theinherent viscosity proscribed herein and not the epoxide equivalent orthe epoxide equivalent and not the inherent viscosity, none of whichexhibit the characteristics of polymers possessing the combinedproscribed parameters. It is essential to this invention that thecopolymer be prepared under conditions wherein polymerization proceedssubstantially via the double bonds to a molecular weight (defined byinherent viscosity) as proscribed while at the same time providingsufficient epoxy groups (defined by epoxide equivalent per 100 grams ofpolymer) as proscribed. It has been found that copolymers having thecombined proscribed epoxide equivalent and inherent viscosity becomeinsoluble at a faster rate upon exposure to irradiation than copolymersexhibiting only one of the proscribed epoxide equivalent or inherentviscosity. Variation from reaction conditions may result in either a lowmolecular weight (low inherent viscosity) polymer having an epoxideequivalent within the proscribed limits which cures at an unacceptablyslow rate or in a high molecular weight polymer (high inherentviscosity) accompanied by a loss of epoxide groups (low epoxideequivalent) which results in a difficulty soluble or insoluble productwhich is either not soluble enough to be used at all or is extremelyslow and difficult to develop. It is believed that those copolymersoutside the parameters of this invention may be the result of prematurecrosslinking of the growing free radical copolymer via the epoxy groupsrather than via the ethylenically unsaturated double bonds as desired.Additionally, uncontrolled increase in chain length of the growingfree-radically initiated methacrylate and allylic portions of themonomer and polymers in the reaction mixture may result in unusuallyhigh molecular weight polymers that are not useful according to theinvention.

The critical epoxide equivalent and inherent viscosity of the copolymersare selectively controlled by the reaction conditions in terms oftemperature and relative molar proportions of the reacting monomers andcatalysts. In general, copolymers exhibiting the necessary viscosity andepoxide equivalent may be obtained when employing from about a 4 to 5molar excess of the glycidyl methacrylate, the preferred proportionsbeing within the range of about 4.5-5.0 moles of glycidyl methacrylateper mole of allyl glycidyl ether.

The copolymerization is conducted in the presence of a polymerizationcatalyst which is a free radical generator and which facilitatescopolymerization via the double bonds thus rendering a product havingpendant epoxy groups suitable for further cationic polymerization viaopening of the epoxy groups initiated by the radiation-sensitiveinitiators. Examples of such catalysts include benzoyl peroxide, azo-bis(isobutyronitrile), p-chlorobenzoyl peroxide, t-butylperoxyoctoate,t-butylperoxy maleic acid, lauroyl peroxide, peroxide, etc. of whichbenzoyl peroxide is the preferred catalyst. Generally, the catalyst isemployed in amounts ranging from 0.40 to 0.60 mol%, based on the molarconcentration of the monomers and is preferably from 0.50 to 0.55 mol%.

The reaction may preferably be carried out in various solvents whichhave boiling points below 100° C. It is necessary that either solventsof higher boiling points be excluded or the temperature controlled at100° C or below since it has been found that reaction temperatures above100° C lead to higher molecular weight copolymers which do not exhibitthe properties of the desired copolymer and particularly since highertemperatures are more likely to cause opening of oxirane (epoxide) ringsand thereby cause undesirable polymerization via the epoxy rings insteadof via the double bonds. Examples of suitable reaction solvents includemethyl ethyl ketone, acetone, dimethyl ether of diethylene glycol,monochlorobenzene, o-chlorotoluene, o-dichloro-toluene, acetonitrile,butyronitrile, etc. and mixtures thereof of which methyl ethyl ketone ispreferred.

Copolymers are prepared by admixing the monomers in a solvent containingthe polymerization catalyst after which the reaction mixture is heatedto reflux and maintained at reflux temperature for a period of about 3to 5 hours. Preferably, a small portion of the catalyst is addedinitially with the major proportion being added after reflux hasstarted. The reaction mixture is subsequently allowed to cool to roomtemperature and the copolymer is precipitated from a suitable solventsuch as methanol, ethanol, isopropanol or like compound which is asolvent for the catalyst and unreacted monomers but in which thecopolymer is insoluble. The product is then dried at temperaturesranging from room temperature up to about 60° C. Substantially higherdrying temperatures are to be avoided to eliminate undesirablecrosslinking, increases in molecular weight or insolubilization (furtherpolymerization) of the copolymer. The following example illustrates atypical preparation of copolymers of the invention:

EXAMPLE 1

Into a 3000 ml. resin flask equipped with a reflux condenser,thermometer, stirrer assembly and addition funnel are placed 360 g. ofglycidyl methacrylate, 60 g. allyl glycidyl ether, 750 ml. of methylethyl ketone, and 0.982g. of benzoyl peroxide. The reaction solution isstirred vigorously while heating to reflux. Upon commencement ofrefluxing, a solution containing 2.97g. of benzoyl peroxide in 300 ml.of methyl ethyl ketone is added slowly from the addition funnel over aperiod of about 1 1/2 hours. The temperature at reflux is about 88° Cand is thus maintained, with stirring, over a total refluxing time of 5hours after which the reaction mixture is permitted to cool to roomtemperature. Following cooling, 200 ml. of additional methyl ethylketone is added with stirring after which the solution is filtered andadded slowly, preferably drop-wise, to 8 liters of methanol. The thusprecipitated white product is collected and washed thoroughly withmethanol after which it is suction dried at room temperature. There isobtained 195g. of a copolymer having an inherent viscosity of about 0.29(indicative of a molecular weight of about 5030) when determined inbutyronitrile at 25° C and an epoxy equivalent of 0.65 equiv./100g. ofpolymer.

II. Copolymer-Catalyst Compositions and Polymerization thereof

In accordance with the present invention, glycidyl methacrylate-allylglycidyl ether copolymers are admixed with a Lewis acid catalystprecursor. The resulting mixture, at a convenient time subsequently, issubjected to the application of energy, such as actinic or electron beamirradiation, to release the Lewis Acid catalyst in sufficient amounts toinitiate the desired polymerization reaction.

The materials utilized as latent polymerization initiators in theprocess and compositions of the present invention areradiation-sensitive catalyst precursors which decompose to effectpolymerization upon application of energy. The energy required foreffective decomposition may be thermal energy, applied by heating, ormay be energy applied by bombardment with charged particles, notably byelectron beam irradiation. Preferably, however, the catalyst precursorsare photosensitive and the required energy is imparted by actinicirradiation which is most effective at those regions of theelectromagnetic spectrum at which there is high absorption ofelectromagnetic energy by the particular catalyst precursor used. Morethan one of these types of energy may be applied to the system, e.g.ultraviolet light irradiation followed by electron beam irradiation. Itis a unique feature of the copolymers of the invention that irradiationalone without subsequent heating is sufficient to effect a rapid andsatisfactory cure.

The radiation-sensitive Lewis acid catalyst precursors are aromaticdiazonium salts of complex halogenides which decompose upon applicationof energy to release a halide Lewis Acid. The aromatic diazonium cationmay be represented generally as (Ar-N═N)⁺, where the aryl group Ar,which may be an alkaryl hydrocarbon group, is bonded to the diazoniumgroup by replacing one of the hydrogen atoms on a carbon atom of thearomatic nucleus, and where the aryl group ordinarily carries at leastone pendant substituent for greater stability of the cation. Thus thependant substituent may be alkyl, or another substituent, or both. Thecomplex halogenide anion may be represented by (MX_(n+) m)^(-m). Thus,the photosensitive salt and its decomposition upon actinic irradiationmay be depicted as follows: ##STR1## where X is the halogen ligand ofthe complex halogenide, M is the metallic or metalloid central atomthereof, m is the net charge on the complex halogenide ion, and n is theoxidation state of M and the number of halogen atoms in the halide Lewisacid compound released. The Lewis acid halide MX_(n) is an electron pairacceptor such as FeCl₃, SnCl₄, PF₅, AsF₅, SbF₃, BiCl₃, and BF₃ whichupon suitable irradiation of the diazonium complex salt is released insubstantial quantities and initiates or catalyzes the polymerizationprocess, wherein the copolymeric material is polymerized or cured as theresult of the actinic irradiation.

The diazonium compounds of the present invention may be prepared usingprocedures known in the art, and such preparation forms no part of thepresent invention. Thus, for example, chlorometallic halogenidecomplexes may be prepared in accordance with the method set forth by Leeet al in Journal of the American Chemical Society, 83, 1928 (1961).

Exemplifying a procedure of general utility, arenediazoniumhexafluorophosphates can be prepared by diazotizing the correspondinganiline with NOPF₆, made by combining HCl and NaNO₂ with subsequentaddition of hydrogen hexafluorophosphate (HPF₆) or of ahexafluorophosphate salt, or they can be prepared by addition of ahexafluorophosphate salt to another diazonium salt to effectprecipitation. As a further example, various morpholinoaryl complexes,containing the group ##STR2## can be prepared either from the anilinederivative or by adding an aqueous solution of a metal salt of thedesired complex halogenide to a solution of morpholinobenzenediazoniumtetrafluoroborate.

Illustrative of the aromatic diazonium cations comprised in thephotosensitive catalyst salts utilized in accordance with the presentinvention are the following:

p-chlorobenzenediazonium

2,4-dichlorobenzenediazonium

2,5-dichlorobenzenediazonium

2,4,6-trichlorobenzenediazonium

2,4,6-tribromobenzenediazonium

o-nitrobenzenediazonium

p-nitrobenzenediazonium

4-nitro-o-toluenediazonium

(2-methyl-4-nitrobenzenediazonium)

2-nitro-p-toluenediazonium

(4-methyl-2-nitrobenzenediazonium)

6-nitro-2,4-xylenediazonium

(2,4-dimethyl-6-nitrobenzenediazonium)

2-chloro-4-(dimethylamino)-5-methoxybenzenediazonium

4-chloro-2,5-dimethoxybenzenediazonium

2,4',5-triethoxy-4-biphenyldiazonium

(2,5-diethoxy-4-(p-ethoxyphenyl)benzenediazonium)

2,5-dimethoxy-4'-methyl-4-biphenyldiazonium

(2,5-dimethoxy-4-(p-tolyl)benzenediazonium)

2,5-diethoxy-4-(phenylthio)benzenediazonium

2,5-diethoxy-4-(p-tolylthio)benzenediazonium

p-morpholinobenzenediazonium

2,5-dichloro-4-morpholinobenzenediazonium

2,5-dimethoxy-4-morpholinobenzenediazonium

4-(dimethylamino)-1-naphthalenediazonium

Illustrative of the complex halogenide anions comprised in thephotosensitive catalyst salts utilized in accordance with the presentinvention are the following:

tetrachloroferrate(III), FeCl₄ ⁻

hexachlorostannate(IV), SnCl₆ ²⁻

tetrafluoroborate, BF₄ ⁻

hexafluorophosphate, PF₆ ⁻

hexafluoroarsenate(V), AsF₆ ⁻

hexafluoroantimonate(V), SbF₆ ⁻

hexachloroantimonate(V), SbCl₆ ⁻

pentachlorobismuthate(III), BiCl₅ ²⁻

A selection of aromatic diazonium salts of complex halogenides is listedin Table I. Many of the salts listed have been found to be well adaptedor superior for use as latent photosensitive polymerization initiatorsin the process and compositions of the present invention, based onthermal stability, on solubility and stability in the epoxy formulationsand solvents used, on photosensitivity, and on ability to effectpolymerization with the desired degree of curing after adequate actinicirradiation. Following the name of each aromatic diazonium halogenide isits melting point or decomposition temperature in degrees centigrade,and wavelengths or electromagnetic radiation, in nanometers, at which itexhibits absorption maxima.

                                      TABLE I                                     __________________________________________________________________________                        M.P.,   Abs'n Max.,                                                           ° C.                                                                           nm.                                               __________________________________________________________________________    2,4-dichlorobenzenediazonium tetra-                                                               62-64   259, 285, 360                                     chloroferrate(III)                                                            p-nitrobenzenediazonium tetrachloro-                                                              93-95   243, 257, 310,                                    ferrate(III)                360                                               p-morpholinobenzenediazonium tetra-                                                               121.5   240, 267, 313,                                    chloroferrate(III)          364                                               2,4-dichlorobenzenediazonium hexa-                                                                190     285                                               chlorostannate(IV)                                                            p-nitrobenzenediazonium hexa-                                                                     126     258, 310                                          chlorostannate(IV)                                                            2,4-dichlorobenzenediazonium tetra-                                                               152     285, 325-340                                      fluoroborate                (shoulder)                                        p-chlorobenzenediazonium hexa-                                                                    162-164 273                                               fluorophosphate                                                               2,5-dichlorobenzenediazonium hexa-                                                                dec. 140                                                                              264, 318                                          fluorophosphate                                                               2,4,6-trichlorobenzenediazonium                                                                   240-250 294, 337                                          hexafluorophospate                                                            2,4,6-tribromobenzenediazonium                                                                    245-260 306                                               hexafluorophosphate                                                           p-nitrobenzenediazonium hexa-                                                                     156 (178)                                                                             258, 310                                          fluorophosphate                                                               O-nitrobenzenediazonium hexa-                                                                     161.5                                                     fluorophosphate                                                               4-nitro-o-toluenediazonium hexa-                                                                  123 (138)                                                                             262, 319                                          flurorphosphate                                                               p-N-morpholinobenzene diazonium                                                                   155 (163)                                                                             257, 375                                          fluoroborate                                                                  p-Nitrobenzene diazonium fluoro-                                                                  140 (148-50)                                                                          258, 311                                          borate                                                                        2,5-diethoxy-4-(p-tolylthio)-                                                                     150 (157)                                                                             354, 403                                          benzene diazonium fluoroborate                                                2-nitro-p-toluenediazonium hexa-                                                                  164-165 286                                               fluorophosphate                                                               6-nitro-2,4-xylenediazonium hexa-                                                                 150     237, 290                                          fluorophosphate                                                               p-morpholinobenzenediazonium hexa-                                                                162 (181).sup.1                                                                       377                                               fluorophosphate                                                               4-chloro-2,5-dimethoxybenzenedia-                                                                 168-169 243 (shoulder)                                    zonium hexafluorophosphate                                                                        (198-208)                                                                             287, 392                                          2,5-dimethoxy-4-morpholinobenzene-                                                                Above   266, 396                                          diazonium hexafluorophosphate                                                                     135                                                       2-chloro-4-(dimethylamino)-5-meth-                                                                111     273, 405                                          oxybenzenediazonium hexafluoro-                                               phosphate                                                                     2,5-dimethoxy-4-(p-tolylthio)ben-                                                                 146 (155)                                                                             358, 400                                          zenediazonium hexafluorophosphate                                             2,5-diethoxy-4-(p-tolylthio)ben-                                                                  147 (150)                                                                             223 (shoulder),                                   zenediazonium hexafluorophosphate                                                                         247, 357, 397                                     2,5-dimethoxy-4'-methyl-4-biphenyl-                                                               167     405                                               diazonium hexafluorophosphate                                                 2,4',5-triethoxy-4-biphenyldiazonium                                                              136     265, 415                                          hexafluorophosphate                                                           4-(dimethylamino)-1-naphthalenedia-                                                               148     280, 310, 410                                     zonium hexafluorophosphate                                                    p-nitrobenzenediazonium hexafluoro-                                                               141-144 257, 310                                          arsenate(V)         (161)                                                     p-morpholinobenzenediazonium hexa-                                                                162     257, 378                                          fluoroarsenate(V)   (176-177)                                                 2,5-dichlorobenzenediazonium hexa-                                                                161.162.5                                                                             238, 358                                          fluoroantimonate(V)                                                           p-nitrobenzenediazonium hexafluoro-                                                               140-141 257, 308                                          antimonate(V)                                                                 p-morpholinobenzenediazonium hexa-                                                                153     254, 374                                          fluoroantimonate(V) (177.5-180.5)                                             2,4-dichlorobenzenediazonium hexa-                                                                178-180 279, 322                                          chloroantimonate(V)         (shoulder)                                        2,4-dichlorobenzenediazonium penta-                                                               193.5-195                                                                             285, 313                                          chlorobismuthate(III)                                                         o-nitrobenzenediazonium penta-                                                                    166.5-168                                                                             285, 313                                          chlorobismuthate(III)                                                         __________________________________________________________________________     Note 1.                                                                       The melting points given in Table I were determined generally by the usua     visual capillary tube method; in most cases discoloration began below the     observed melting point temperature with frothing decomposition at that        temperature. In some cases melting points or exotherms were determined        also by differential thermal analysis under nitrogen gas, and the             temperatures so determined are given in parentheses. The wavelengths of       absorption maxima in the ultraviolet-to-visible range were determined wit     the diazonium complex salt dissolved in acetonitrile.                    

Referring to equation I hereinabove showing the photolytic decompositionof the catalyst precursor, the halide Lewis acid MX_(n) released reactswith the epoxide material with a result exemplified by the following:##STR3## The cationic catalyst is believed to act by cleaving acarbon-oxygen epoxy bond, initiating growth of a polymeric chain orpermitting formation of a cross-linkage. A general application of theprocess embodied by equations I and II can be as follows: a diazoniumcomplex salt, for example, as identified hereinabove, is admixed, withthe use of a suitable solvent, with the epoxy copolymer. The mixture isthereafter coated on a suitable substrate such as a metal plate,plastic, or paper, and the substrate is exposed to ultraviolet orelectron beam radiation. On exposure the diazonium compound decomposesto yield the Lewis Acid catalyst, which initiates the polymerization ofthe expoxy copolymer. The resulting polymer is resistant to mostsolvents and chemicals.

The source of radiation for carrying out the method of the presentinvention can be any suitable source, such as the actinic radiationproduced from a mercury, xenon, or carbon arc, a beam from a lasersource, for example a He-Cd laser, or the electron beam produced in orfrom a cathode ray gun. The only limitation placed on the radiationsource used is that it must have an energy level at the irradiated filmsufficient to impart to the polymerizable system energy at an intensityhigh enough to reach the decomposition level of the photosensitivecompounds. As previously noted, the wavelength (frequency) range ofactinic radiation is chosen to obtain sufficient absorption of energy toexcite the desired decomposition.

For an imaging system, the mixture, which may contain a suitable solventin substantial proportions, is coated on a metal plate, dried ifnecessary to remove solvent present, and the plate is exposed toultraviolet light through a mask or negative. The light initiatespolymerization which propagates rapidly in the exposed image areas. Theresulting polymer in the exposed areas is resistant to many or mostsolvents and chemicals, while the unexposed areas can be washed withsuitable solvents to leave a reversal image of an epoxy polymer in thisembodiment.

Exemplary of such solvents suitable for development of the image arebutyronitrile, butyronitrile-toluene mixtures, (preferably 1:1mixtures), trichloroethylene-acetones, methyl ethyl ketone,cyclohexanone, tetrachloroethane-acetone, acetone-isopropanol,butyronitrile-o-chlorotoluene wherein the mixtures are preferably in 1:1or 2:3 relative proportions.

The procedures for mixing the radiation-sensitive compositions of thepresent invention using the copolymeric epoxide are relatively simple.The epoxide is combined with the catalyst precursor in a suitable inertvolatile solvent. By such a suitable solvent is meant any solventcompound or mixture which boils below about 190° C and which does notreact appreciably with the epoxide or the catalyst precursor. Examplesof such solvents include acetone, methyl ethyl ketone, dimethyl ether ofdiethylene glycol (bis(2-methoxyethyl ether), monochlorobenzene,o-chlorotoluene, o-dichlorotoluene, acetontrile, butyronitrile,cyclohexanone, tetrahydrofuran or mixtures thereof and also mixtures ofthese solvents with other compounds in which the copolymer issubstantially insoluble such as toluene, ethyl ether, anisole,1,1,2,2-tetrachloroethane and trichloroethylene.

The amount of catalyst precursor employed should be sufficient to insurecomplete polymerization. It has been found that quite satisfactoryresults are obtained by providing a diazonium complex salt in amount byweight from about 0.5% to about 5% of the catalyst precursor relative tothe weight of the polymerizable material provided, about 1% or less ofthe precursor being amply effective.

It may be desirable to include in the composition an inert pigment orfiller, which may be present in even a major proportion by weight.Inclusion of such inert ingredients usually makes advisable aproportionate increase in the optimum amount of catalyst precursoradded. Nevertheless, the amount of the precursor needed rarely exceeds5% of the entire weight of the composition.

The following examples will serve to further illustrate the presentinvention.

EXAMPLE 2

a. The following formulation was prepared:

5 g. of glycidyl methacrylate-allyl glycidyl ether copolymer of Example1

5.0 g. of o-chlorotoluene

44.4 ml. of butyronitrile

0.25 g. of 2,5-diethoxy-4-(p-tolylthio) benzene diazoniumhexafluorophosphate

The filtered solution was whirl-coated onto dichromated aluminum at arate of 60 RPM. Sample strips cut from the plate were exposed to a xenonlamp through a Kodak No. 2 step tablet for the times indicated below.

b. For purposes of comparison, a formulation similar to formulation (a)but utilizing as the epoxide component ECN 1299, an epoxy cresol novolachaving a molecular weight of 1270 and an epoxide equivalent of 0.425 per100 g. of polymer (available commercially from CIBA PharmaceuticalProducts) was prepared as above. The exposure and results are asindicated below:

1. Five exposure units (an exposure unit is approximately equal to onesecond exposure)

After immediate development of the above sample strips of formulation(a) in acetone-methyl ethyl ketone solution, six steps were reproduced.The coating of formulation (b) washed off. It required 55 units ofexposure to reproduce 6 steps with formulation (b).

To demonstrate superior adhesion properties of the above formulation(a), the coating of a sample strip was scratched and submerged in waterfor 20 minutes. A sample strip prepared from formulation (b) wasidentically treated.

After drying, a strip of Scotch brand mylar pressure-sensitive tape waspressed over the coated and scratched portions of the plates and pulledoff. None of the coating derived from formulation (a) was lifted off.The coating derived from formulation (b) did not adhere at all and wasreadily removed by lifting the tape.

2. Eight exposure units

An eight second exposure was made on samples of plates derived fromformulations (a) and (b) respectively. The individual plates wereimmediately sliced longitudinally to give two equally exposed strips ofplate.

Results with formulation (a):

Immediate development of one of these strips gave 7 steps.

Development of the second after 30 minutes gave 9 steps indicating agrowth of 2 steps due to continuing reaction.

Results with formulation (b):

Immediate development of one of the strips of this formulation resultedin washing away of the entire coating. It was determined that greaterexposure times were necessary with this formulation to obtain ameaningful number of steps. (In general, reproduction of at least 6steps is required to demonstrate usefulness for preparation of lithoplates, for example). The necessary exposure for this formulation wasdetermined to be 80 exposure units to obtain 7 steps and the step growthobserved with this formulation was 5 steps due to continuing reaction.

This example illustrates the superiority of the copolymers of theinvention over one of the most efficient commercial epoxide materials,ECN 1299, when employed as a photoresist in exhibiting greater adhesivestrength to aluminum, in requiring less exposure (a measure of itssuperior photosensitivity) and in exhibiting a reduction in step growthafter exposure, (a measure of the rapidity and completeness of itscure). When either of commercially available epoxides such as EPON 1009,a bis-phenol A-glycidyl ether polymer or Araldite 6054 are substitutedfor ECN 1299 of formulation (b), the results are even less comparable tothose received with formulation (a) since these resins have been foundto be less photosensitive than the ECN 1299 resin compared above.

Offset printing plates made with formulation (a) showed no signs ofadhesion failure at least up to 88,000 impressions, an indication of thedurability of the coatings produced.

EXAMPLE 3

The following formulations were prepared:

(a) 9.0 g. glycidyl methacrylate-allyl glycidyl ether copolymer havingan inherent viscosity of 0.29 and an epoxide equivalent of 0.65

13 g. o-chlorotoluene

78 g. butyronitrile

0.450 g. 2,5-diethoxy-4-p-tolylthio benzene diazoniumhexafluorophosphate

(b) 9.0 g. polyglycidyl methacrylate having an inherent viscosity of0.13 and epoxide equivalent of 0.65

0.450 g. 2,5-diethoxy-4-p-tolylthio benzene diazoniumhexafluorophosphate

13 g. o-chlorotoluene

78 g. butyronitrile

In each case the solutions were treated with Cellite 503 filter aid,filtered through paper and then through a 7u millipore filter.

Solutions of the above formulations (a) and (b) were coated onto apolyethylene terephthalate photographic film base (availablecommercially under the trademark Cronar). After drying, the coatingswere exposed to an ultraviolet light source through a Kodak No. 2 steptablet for 10 seconds and developed employing a mixture oftrichloroethylene and acetone. The results were that 12 steps werereproduced with the coating of formulation (a), while 7 steps werereproduced with the coating of formulation (b). The results indicatethat the glycidyl methacrylate-allylglycidyl ether of this invention is5 times as photosensitive as the polyglycidyl methacrylate of the priorart even when selected to have the same epoxide equivalent.

EXAMPLE 4

To illustrate the criticality of the various parameters relative toepoxide equivalent and inherent viscosity in the present invention,copolymers were prepared employing the procedure of Example 1 withdeviations therefrom as indicated in the Table which follows. All of thepreparations utilized methyl ethyl ketone as reaction solvent andbenzoyl peroxide as catalyst. With the exception of the firstpreparation, all components were placed in the reaction vessels at onetime and then heated to reflux. In preparation 1, the procedure ofExample 1 was followed wherein the major portion of catalyst was addeddissolved in methyl ethyl ketone after refluxing had begun. Inpreparation 10, a trace amount (200 ppm) of p-methoxy phenol was addedto control the molecular weight (inherent viscosity). The inherentviscosity was obtained in butyronitrile at 25° C.

Copolymers with the epoxide equivalents and inherent viscositiesindicated were formulated as in Example 2 containing the same amounts ofsolvents and photosensitive initiator indicated therein. Theformulations were applied to a substrate and the relative sensitivitywas obtained from the number of steps of a Kodak No. 2 step tabletremaining on the substrate after 10 seconds of exposure to a xenon lampand solvent development for 2 minutes employing a 3:1 mixture oftrichloroethylene-acetone as the developing solvent, followed by a finalrinse in toluene.

                                      TABLE II                                    __________________________________________________________________________    Preparation                                                                           Mole Ratio                                                                           Mole % Per-                                                                           Epoxide Equiv.                                                                         Inherent                                                                            No. Steps after 10                                                                       Relative                     No.     GMA / AGE                                                                            oxide Catalyst                                                                        Per 100 g.                                                                             Viscosity                                                                           Second Exposure                                                                          Sensitivity                  __________________________________________________________________________    1       4.82   0.53    0.65     0.29  12         1.00                         2       4.82   0.53    0.66     0.50  10         0.83                         3       4.82   0.53    0.69     0.27  10         0.83                         4       4.82   0.53    0.65     0.33  12         1.00                         5       4.82   0.15    0.45     0.59  Did not develop                                                               cleanly; Exposed                        (Comparative)                         Film poor and                                                                            --                                                                 hazy; Unexposed                                                               film incompletely                                                             developed; unex-                                                              posed areas tend                                                              to cure in the                                                                dark.                                   6       1.20   0.41    0.74     0.22  6          0.50                         (Comparative)                                                                 7       4.82   0.53    0.64     0.17  4-5        0.33-0.41                    (Comparative)                                                                 8       1.00   0.53    0.62     0.12  1          .083                         (Comparative)                                                                 9       4.82   0.28    0.66     0.10  3          .25                          (Comparative)                                                                 10      4.82   0.53    0.65     0.10  3          .25                          (Comparative)                                                                 __________________________________________________________________________

It can thus be seen that the combined parameters relative to the epoxyequivalent and inherent viscosity of the copolymers of the invention areof critical importance to the successful practice of the invention, thesuperior photosensitivity of those copolymers having properties withinthese parameters being readily observed.

The present invention provides copolymers of varying viscosity andsolubility in coating and processing solvents which permits tailoring ofthe particular copolymer for the particular application. For example,copolymers within the preferred range of inherent viscosity having anepoxide equivalent of at least about 0.65 will exhibit better solubilitythan higher viscosity copolymers, are readily filtered through Milliporefilters of a micron or less in size and are particularly useful forapplications demanding high resolution images. As the inherent viscosityexceeds the 0.38 level, the solutions are not as readily soluble, aremore difficult to filter through standard filters of submicron size andare not as useful in high image resolution applications. On the otherhand, where high resistance to abrasion or etchants or solvent actionbecomes the more important consideration as where the material is usedon a chrome photomask or is itself used as a photomask, the higherviscosity copolymers exhibiting the proscribed epoxy equivalent are moreuseful since they have higher resistance to abrasion and strongetchants.

The polymers produced by polymerizing the copolymers of the presentinvention are useful in a wide variety of applications in the field ofgraphic arts due to their superior adhesion to metal substrates,excellent resistance to most solvents and chemicals and capability offorming high resolutions images. Among such uses are photoresists forchemical milling, gravure images, offset plates, letterpress plates,stencil-making disclosed discloed and claimed in application Ser. No.283,629, filed Aug. 25, 1972 entitled "Epoxy Photopolymer DuplicatingStencil" now U.S. Pat. No. 3,826,650 issued July 30, 1974), microimagesfor printed circuitry, micro-images for information storage, thermosetvesicular images, decoration of paper, glass and packages andlight-cured coatings, photofabrication and photoetching. The copolymersof the invention have been discovered to be particularly effective foruse in recording and storing information derived form a laser source.

The following examples illustrate use of the copolymers for various ofthese applications.

EXAMPLE 5

A formulation was prepared consisting of 50 g. of a 15% solution of thecopolymer of Example 1 in butyronitrile and 0.37 g. of2,5-diethoxy-4(p-tolythio) benzene diazonium hexafluorophosphate. Afterfiltering the solution, spin-coatings were made on polyethyleneterephthalate film available commercially as Cronar or Mylar film at aspeed of 200 rpm. A contact print was made on the coated Cronar from a24 X microfiche negative in a vacuum frame. The exposure time was 3seconds using an Aristo model B3642 ultraviolet grid lamp. Developmentin a solution of butyronitrile or a 1:1 mixture of butyronitrile andtoluene followed by a rinse in toluene, yielded an excellent colorlesspositive image with no frosting. Development of another sample in a 3:1mixture of trichloroethylene and acetone resulted in an image withslight frosting.

If desired, the image can be dyed employing a dye solution such asCIBA's Orasol Black Dye in trichloroethylene followed by a rinse intrichloroethylene.

The compositions described in Part II hereinabove may be employed forrecording and storing information from a laser source as illustratedhereinbelow. When utilized as holograms, they are particularly valuable,since the copolymer forms a clear film in the absence of catalyst. Thisis important since it is desired to avoid absorption of light goingthrough in the reconstruction of the hologram. Utilizing thecompositions of this invention, once they are polymerized adequately anddeveloped, the copolymer is a clear film. Holograms derived from thecompositions of the invention are characterized by having high imageresolution capacity, images prepared are stable and unaffected byhumidity, temperature and surface abrasion; they are easily, rapidly andeconomically prepared and once prepared are long-lived.

Holograms and other articles for recording information from a lasersource according to the present invention may be prepared employingmeans conventional in the art. An example of such apparatus may be asdescribed and illustrated in U.S Pat. No. 3,410,203 issued Nov. 12,1968. Thus, suitable apparatus includes means for supplying a coherentbeam of radiation derived from a laser source to a substrate coated withthe compositions of Part II hereinabove. To prepare a holographic imageon said coated substrate, data may be photographed on a transparency,for example as derived from an electronic photocomposition system suchas RCA Videocomp 70/820. The transparency is positioned so that aninformation beam of light from a laser source is projected thereon. Theinformation beam may first be scattered through a diffuser, and areflective mirror positioned intermediate the diffuser and the laser,that splits the light beam from the laser into a reference beam and aninformation beam, may be employed. The reference beam is directed onto amirror to provide a reference path from the laser source to aphotosensitive film comprising the compositions of the presentinvention. The mirror is positioned so that the reference beam forms anangle with the horizontal. The information beam travels through thetransparency directly to the photosensitive composition or hologram. Thecombination of the reference beam and the information beam travelling bydifferent paths to the hologram produces interference patterns on thehologram to cause the print date in the transparency to be recorded as aholographic image on the hologram. The photosensitive compositions ofthis invention are hardened onto the surface and in the volume of thehologram at those places where light from the reference beam andinformation beam interfere constructively and the hologram is developedemploying the developing solvents disclosed hereinabove.

Any suitable support to which the cured polymer will adhere may form thesurface of the hologram including metal, glass, plastic, silicon wafers,paper, rubber, etc.

Coatings may be applied to said supports at various rates orthicknesses. In general, thicknesses of 0.1 um to 2 um have beensatisfactorily employed in our work. Additionally, information receivedby laser scanning may be recorded on plastic tape and other substratessuch as metal, paper, rubber, glass, silicon wafers, etc.

It is to be understood that the particular laser apparatus andcombination thereof forms no part of the present invention and any ofconventional systems may be employed. Thus, a single laser may beemployed, as, for example, a gas laser such as a carbon dioxide laser orany of well known lasers. Alternatively, a laser, for example, a 4416Ahelium-cadmium laser may be employed with a separate second laser beamto provide the interference pattern. It is preferred that the wavelengthemployed be within the range of maximum sensitivity of the catalyst, forexample, from 3500-4500A for the preferred 2,5-diethoxy-4-(p-tolylthio)benzene diazonium hexafluorophosphate. The specific wavelength rangesfor maximum sensitivity will of course depend on the particular catalystand may be readily ascertained from the absorption maxima listed inTable I.

The developed hologram may be subsequently subjected to furthertreatment for adaptation to various applications. For example, it may beemployed in video tape systems such as the RCA Selectavision wherein itmay be electrolytically plated with nickel which may then be strippedaway bearing an impression of the hologram. Such impression may then beemployed to press out further images on plastic tape such as vinyl orpolyethylene.

Alternatively and uniquely, impression images may be made by a novelprocedure which eliminates the need for a nickel master employing thehologram or photoresist image directly to replicate impressed images onvarious thermoplastic materials. In this procedure, the hologram orphotoresist is prepared and developed as described above. The hologramor photoresist image is heated to a temperature of about 120° to 130° C,and is contacted with a thermoplastic material while pressure such asthat exerted by contact rollers or even hand is applied thereto, leavingreplicated impressions of the hologram or photoresist image on thethermoplastic material.

Suitable thermoplastic materials to receive impressions from thehologram or photoresist may be materials having a softening point belowthe softening point of the substrate bearing the photoresist image andthat of the photoresist itself. In general, such materials havingsoftening points below 150° C, preferably below 135° to 140° C, may beutilized. Exemplary of such materials are polyethylene terephthalate,polyethylene, polypropylene, polyacrylics, polyvinylchloride,polystyrene, polyvinylidine, chloride, poly(chlorotrifluoroethylene),polytetrafluoroethylene (Teflon), Nylon 6, Nylon 6,6,polycarbonate(Lexan, a polyester derived from bis-phenol A and carbonic acid),cellulose acetate, cellulose acetate butyrate, cellulose, propionate,ethyl cellulose, and polyacetal resins. Such materials may be employedin any convenient form or shape, for example, as sheet, tape, rolls,ribbons, etc.

The following examples are given to illustrate further embodiments ofthe invention:

EXAMPLE 6

A microfiche contact print was made as in Example 5 and heated at 130° Cfor 1 hour to effect maximum hardening and curing of the image on thecoated film. The print was then run through a pair of metal rollers withthe copied information in contact with a strip of polyvinyl chloride ofabout 2-3 mils thickness. The roller in contact with the backside of theplastic film bearing the photoresist image to be replicated was heatedto 125° C. After passing between the rollers, the polyvinyl chloridefilm had an intaglio copy of the information on the photopolymer filmcopy pressed into it. Information thus replicated could be read on amicrofiche reader and several copies were made from the one masterphotopolymer film.

EXAMPLE 7

A master solution was made of the following ingredients:

20 g. allyl glycidyl ether - glycidylmethacrylate copolymer of Example 1

20 g. o-chlorotoluene

176 ml. butyronitrile

After all solid material had gone into solution, the solution wasfiltered and percent solids was determined to be about 10.95%. From thismaster solution, a coating solution containing 85.3 g. master solutionand 0.467 g. 2,5-diethoxy-4(p-tolylthio)benzene diazoniumhexafluorophosphate was prepared and filtered through a double layer ofpaper towels. The solution was whirl coated onto large glass slides at60 rpm to a thickness of 0.06 mil. at a low heat setting on the whirlcoater for 15 minutes. The coated slides were used after 24 hours asfollows to prepare a hologram:

Three coated slides were exposed to a 4400 A He-Cd laser employing asecond laser to provide the interference pattern. Each slide was thendeveloped in a 1:1 methylethylketone-trichloroethylene solution.

The first slide was positioned with information and reference beams at a23° angle and exposures of 1, 1/2, 1/5, 1/10 and 1, 2, 5, 10 secondsduration in two rows. After development, the interference patterns couldbe seen as with the first slide but were not as sharply defined.

The extent of resolution was determined, employing the Bragg equation,to be at least 1000 line pair/^(mm).

EXAMPLE 8

A solution was made consisting of 0.576 g. of2,5-diethoxy-4-(p-tolylthio)benzene diazonium hexafluorophosphate in122.6 g. of a 9.42% solution of the copolymer of Example 1 inbutyronitrile. After filtering the solution, it was used to spin coatglass slides at 800 rpm. A coated slide was exposed for 5 seconds at thepoint of reconvergence of the split beam of a Coherent Radiation Model53A Argon ion laser. The beam separation angle at this point was 20° andthe power of the laser beam was about 100 mw at 363.8 mm. The exposedspot was developed in a solvent composed of 3 volumes trichloroethyleneand 1 volume of acetone. A bright diffraction grating resulted whichcould be discerned under the microscope as a series of sharp, parallellines. The resolution was calculated to be 954 cycles/mm.

Similar examples were run with additional glass slides or Cronar filmsas substrates employing an optimum copolymer coating thickness of 0.8 to1.2mm. Diffraction efficiencies up to 25% were measured on such slides.in one run, employing a beam separation angle of 87°, thickness of 0.7umand glass as the substrate, a resolution capability up to at least 3700cycles/mm was obtained.

The following example was run to determine the energy requirement forimage-wise crosslinking employing a laser beam as the energy source.

EXAMPLE 9

The formulation of Example 8 was employed to make coatings on Mylar filmat 60 RPM whirler speed. A series of exposure spots were made on thecoating using the laser of Example 8 emitting 250 mw at 351.1 and 363.8mm combined. Using a combination of increasing shutter speeds andfilters of known absorption at these wave lengths, a series of 1.5mm²area exposure spots of diminishing duration and intensity was madeacross the surface of the coated film down to 100 u-secs. equivalentexposure time. The exposed spots were developed in a 3:2 mixture oftrichloroethylene and acetone and when held to a light source, thedeveloped spot could be seen. The ability to develop a visiblephotoresist spot with 100 u-secs. equivalent exposure at 250 mwindicated a calculated energy requirement of 1.27 millijoules/cm². Fromthis data, a laser scanning speed of 20,000 inches per second for a 1mil wide line was indicated.

We claim:
 1. A copolymer of glycidyl methacrylate and allyl glycidylether having pendant epoxy groups, an inherent viscosity of at leastabout 0.25 as measured in butyronitrile at 25° C, an epoxide equivalentof at least about 0.65 epoxide equivalent per 100 grams of polymer andpolymerizable to higher molecular weights through said epoxy groups bythe action of a cationic catalyst; said copolymer being derived fromreaction of a mixture of said monomers consisting of from about 4 toabout 5 moles of glycidyl methacrylate per mole of allyl glycidyl etherin the presence of a catalyst effective to initiate polymerizationthrough ethylenic unsaturation of the monomers in a solvent at areaction temperature below about 100° C.
 2. A polymerizable copolymer asclaimed in claim 1 wherein the inherent viscosity is within the range ofabout 0.25 to about 0.38.
 3. A polymerizable copolymer as claimed inclaim 1 wherein the epoxide equivalent is within the range of about 0.65to about 0.74.
 4. A polymerizable copolymer as claimed in claim 1wherein said catalyst initiating polymerization through ethylenicunsaturation is benzoyl peroxide.
 5. A polymerizable copolymer asclaimed in claim 1 wherein said solvent is selected from the groupconsisting of methyl ethyl ketone, acetone, dimethyl ether of diethyleneglycol, monochlorobenzene, o-chlorotoluene, o-dichlorotoluene,acetonitrile, butyronitrile and mixtures thereof.
 6. A copolymer ofglycidyl methacrylate and allyl glycidyl ether, having pendant epoxygroups, an inherent viscosity of about 0.25 to about 0.38 as measured inbutyronitrile at 25° C, and an epoxide equivalent within the range ofabout 0.65 to about 0.74 epoxide equivalent per 100 grams of polymer andpolymerizable to higher molecular weights through said epoxy groups bythe action of a cationic catalyst; said copolymer being derived fromreaction of a mixture of said monomers consisting of about 4 to 5 molesof glycidyl methacrylate per mole of allyl glycidyl ether in thepresence of a catalyst effective to initiate polymerization throughethylenic unsaturation of the monomers and in a solvent at a temperaturebelow 100° C, said solvent being selected from the group consisting ofmethyl ethyl ketone, acetone, dimethyl ether of diethylene glycol,monochlorobenzene, O-chlorotoluene, O-dichlorotoluene, acetonitrile,butyronitrile and mixtures thereof.
 7. A method for the preparation of acopolymer of glycidyl methacrylate and allyl glycidyl ether, havingpendant epoxy groups, an inherent viscosity of at least about 0.25, asmeasured in butyronitrile at 25° C, and an epoxide equivalent of atleast about 0.65 epoxide equivalent per 100 grams of polymer whichcomprises forming a mixture consisting of from about 4 to 5 moles ofglycidyl methacrylate per mole of allyl glycidyl ether in the presenceof a polymerization catalyst effective to initiate polymerizationthrough ethylenic unsaturation of the monomers and a solvent and heatingsaid mixture at a temperature below about 100° C for a period sufficientto copolymerize said monomers.
 8. A method as claimed in claim 7 whereinsaid catalyst is benzoyl peroxide.
 9. A method as claimed in claim 7wherein said solvent is selected from the group consisting of methylethyl ketone, acetone, dimethyl ether of diethylene glycol,monochlorobenzene, o-chlorotoluene, o-dichlorotoluene, acrylonitrile,butyronitrile and mixtures thereof.
 10. A method as claimed in claim 8wherein a major portion of said ppolymerization catalyst is added afterreflux has begun.
 11. A method for the preparation of a copolymer ofglycidyl methacrylate and allyl glycidyl ether, having pendant epoxygroups, an inherent viscosity of from about 0.25 to about 0.38, asmeasured in butyronitrile at 25° C, and an epoxide equivalent of fromabout 0.65 to 0.74 epoxide equivalent per 100 grams of polymer, whichcomprises forming a mixture consisting of from about 4 to 5 moles ofglycidyl methacrylate per mole of allyl glycidyl ether in the presenceof benzoyl peroxide and a solvent selected from the group consisting ofmethyl ethyl ketone, acetone, dimethyl ether of diethylene glycol,monochlorobenzene, o-chlorotoluene, o-dichlorotoluene, acetonitrile,butyronitrile and mixtures thereof and heating said mixture at atemperature below about 100° C for a period sufficient to copolymerizesaid monomers.